Thread rolling machine

ABSTRACT

A thread rolling machine is disclosed wherein a rotary die has multiple starts of a thread form and workpieces are fed in synchronism so that the starting points of threads on successive workpieces gradually moves around the periphery of the die. By this means all of the thread starts are used in a sequence so that just a few are not subjected to this starting of threading. By this means die life is materially extended. The above description is merely one form of the invention and is not to be construed as limiting on the scope of the invention.

11 3,733,867 1 May 22, 1973 United States Patent n91 Prutton 1,780,608 11/1930 Swanson...................................72/97 [541 THREAD'ROLLING MACHINE Primary ExaminerMilton S. Mehr Attorney-Louis V. Granger [57] ABSTRACT A thread rolling machine is disclosed wherein a rotary Ohio Feh..14, 1972 211 Appl. N5; 225,849

[22] Filed:

die has multiple starts of a thread form and workpieces are fed in synchronisrn so that the starting points of threads on successive workpieces gradually moves around the periphery of the die. By this means all of the thread starts are used in a sequence so that 34 909 WW ..n9 1 7 23 M 2 m mmhm c "mm L C d sum UHF 1 2 1] 2100 555 [[l.

just a few are not subjected to this starting of threading. By this means die life is materially extended. The above description is merely one form of the invention and is not to be construed as limiting on the scope of the invention.

2,666,349 1/1954 Batchelder...............................72/93 19 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION Planetary thread rolling machines have been used with a rotary die and a stationary die shoe. The workpieces, such as bolt blanks, are fed in succession to the entrance end of the stationary shoe and are transported by planetary rolling action between the two dies to roll form a thread thereon. The workpiece generally has a single start thread and might be one-half inch pitch diameter, for example. The rotary die is generally much larger in diameter, for example, 12 inches in order to spread the load onto a larger surface and to reduce the radius of the die at its contact area with the workpiece. The diameter of the die is a function of the pitch diameter of the workpiece for a constant radius stationary die. For the example given above, the ratio of the diameter of the rotary die to that of the workpiece is 24:1.

It has been customary in the prior art planetary roll forming machines that the feeding of workpieces has been synchronized at a definite integral ratio of the rotation of the rotary die. In the above prior art example of a 24:1 ratio the practice was to gear the machine to synchronously feed four or six workpieces per revolution of the rotary die. This was standard practice in the past to always gear the feed cam in such a way that it cycled an integral number of times in relation to one revolution of the rotary die. The feed slide had to cycle an exact three, four, five, six, etc. times per revolution of the rotary die. It has been common knowledge that this was the only way that it could be done. By this means the workpiece always started in synchronism with the start of one of the multiple starts on the rotary die. However, this had the disadvantage that these four starts, for example, of threads on the rotary die were those which broke down and when they did the die life was ended.

Accordingly, an object of the invention is to materially increase die life.

Another object of the invention is to provide a method of gradually changing the starting position around the periphery of a rotary die.

Another object of the invention is to provide a thread rolling machine wherein the starting of thread rolling is synchronized with the start of a multiple start thread yet progressively moves around the die.

Another object of the invention is to provide a planetary thread rolling machine which saves on material in the construction of replacement rotary dies.

Another object of the invention is to provide a planetary thread rolling machine with many more choices of radial thickness of rotary die to be able to choose one of appropriate thickness to savematerial.

SUMMARY OF THE INVENTION The invention may be incorporated in a planetary thread rolling machine comprising, a frame, a rotary die rotatable about an axis relative to said frame and having N starts of threads around the periphery thereof, a second die on said frame, a thread form on said second die substantially equal to that on said rotary die, means to rotate said rotary die, means to feed a succession of workpieces to the area between said rotary and second dies, and synchronizing means synchronizing the feeding of workpieces with a spacing S between workpieces where S is a given multiple of the peripheral spacing between thread starts on he rotary die and where the ratio of N/S is other than an integer.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing, in which:

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is an isometric view of a machine embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The single FIGURE illustrates a machine 11 incorporating the invention. This machine has a frame 12 indicated schematically which journals a rotary die spindle 13. A rotary die holder 14 is fixed to rotate with the spindle 13. A motor 15 is connected by suitable speed reduction linkage I6 to rotate the spindle 13. A rotary die 18 is secured by clamps 17 on the rotary die holder 14. A second die 19 is mounted fixed on the frame 12. This mounting is provided by a die shoe 20 held in an adjustably fixed manner by advancing screws 21 and retracting screws 22 passing through a fixed frame member 23 and engaging the die shoe 20.

The rotary die 18 has a multiple start thread form 24 on the outer periphery thereof, which periphery would be cylindrical except for such thread form. Also, the stationary die 19 has on the inner generally cylindrical surface thereof a substantially similar multiple start thread form 25. These two thread forms may be adjusted relative to each other by the ad-justing screws 21 and 22 so that successive workpieces 26 may be fed to the area between the dies 18 and 19 at the entrance end 28 of the stationary die 19. The second die 19 may extend a suitable distance around the periphery of the rotary die 18, for example, one-sixth, one-fourth or onethird of the distance.

The rotary die 18 rotates about an axis 30 and feed means 31 is provided to feed successive workpieces 26 to the die entrance end 28. This feed means 31 may be a feed chute 32 down which workpieces feed by gravity to the die entrance end 28. A feed slide 33 is periodi cally reciprocated along its length to intermittently feed the next workpiece from the chute 32 into the area between the dies.

Synchronizing means 35 is provided to synchronize the feeding of successive workpieces in accordance with the rotation of the die 18. This synchronizing means 35 accomplishes this by being geared to rotate directly with the spindle 13. A bevel ring gear 36 is fixed on the spindle I3 and meshes with a bevel pinion 37 fixed on a cross shaft 38. A second cross shaft 39 is parallel to shaft 38 and the outer ends of these shafts carry change gears 40 and 41 respectively. Shaft 39 feeds into a right angle 1:1 gear box 42 having an output shaft 43 driving a single lobe cam 44. A cam follower lever dS is pivoted at 46 and has a follower roller 47 moved by the cam 44 and has an actuating roller 48 acting on the feed slide 33.

OPERATION The motor 15 rotates the rotary die 18. Through the synchronizing means 35 the feed means 31 is periodically actuated in timed relation to feed a succession of workpieces 26 to the area between the dies 18 and 19. The machine 11 is provided with change gears 40, 41 which are readily accessible, to provide any desired ratio N/S where N is the number of starts of threads around the periphery of the multiple start thread form 24 and where S is the spacing between successive workpieces expressed as a given multiple of the peripheral spacing between thread starts on the rotary die 18. The prior art considered that the only way this type of machine could be constructed was to have the ratio N/S an integer. The example given above is that if the work piece had a one-half inch pitch diameter and the rotary die had a 12 inch pitch diameter, then the rotary die would have a 24 start thread form in order to produce a single start thread on the workpiece. If such prior art machine had been constructed with a feed cam cycling to feed four workpieces per revolution of the rotary die, then only four out of the 24 thread starts would be those at which threading of successive workpieces commenced. It has been found through long observation that these four thread starts are those which first break down. This means complete die failure and the die must be replaced. it is expensive to replace a rotary die 18 because the threads are first machined, for example, by grinding and then the thread form is hardened to withstand the form rolling of perhaps millions of pieces. The rotary die must be made with precision and care and to have to discard it after only four of the 24 thread starts were broken is an expensive waste, yet a practice which has been followed for decades.

The present machine provides a construction and a method of operation to utilize all 24 of the thread starts on such a rotary die 18 by starting workpieces at each one of these 24 thread starts in a particular repetitious sequence.

The prior art construction considered that the only way to operate a machine of this type was to have the feed slide 33 reciprocate an exact integral number of times per revolution of the rotary die 18. Table A shows this prior art method. The first column N shows the number of thread starts on the rotary die and the second column S shows the spacing between successive workpieces as a given integral multiple of the peripheral spacing between thread starts on the rotary die. The third column lists this ratio'of N/S.

PRIOR ART TABLE A Uses N S N/S Reduced Thread Starts 30 6 30/6 5 24 6 24/6 4 4 3O 5 30/5 6 6 25 5 25/ 5 5 5 2O 5 20/5 4 4 28 4 28/4 7 7 24 4 24/4 6 6 20 4 20/4 5 5 27 3 27/ 3 9 9 24 3 24/3 8 8 2 1 3 2 1/3 7 7 The fourth column shows this numerical fraction reduced to the lowest common denominator which in this case is unity and thus shows that the ratio was always chosen as an integer in this prior art practice. The fifth column lists the number of thread starts which were used as the starting point for workpieces around the periphery of the rotary die. It will be observed that the number in this column is identical to the corresponding numeral in the fourth column. 7

The present invention illustrates that it is not necessary to gear the feed cam in integral numbers per revolution of the rotary die and it is, in fact, desirable to throw the machine out of time. Table B illustrates the machine and method according to the present invention with the same five columns as listed for Table A. Referring to the first row, if N equals 31 and S equals 6 then the ratio N/S is 31/6. This is an irreducible fraction and, accordingly, the fifth column shows that all 31 thread starts are used.

TABLE B Uses N S N/S Reduced Thread Starts 31 6 31/6 31 29 6 29/6 29 28 6 28/6 14/3 14 27 6 27/6 9/2 9 26 6 26/6 13/3 13 25 6 25/6 25 23 6 23/6 23 22 6 22/6 11 21 6 21/6 7/2 7 20 6 20/6 10/3 10 19 6 19/6 19 31 5 31/5 31 29 5 29/5 29 28 5 28/5 28 27 5 27/5 27 26 5 26/5 26 24 5 24/5 24 23 5 23/5 23 22 5 22/5 22 21 5 21/5 21 19 5 19/5 19 31 4 31/4 31 29 4 29/4 29 27 4 27/4 27 26 4 26/4 13/2 13 25 4 25/4 25 23 4 23/4 23 22 4 22/4 11/2 11 21 4 21/4 21 19 4 19/4 19 32 3 32/3 32 31 3 31/3 31 29 3 29/3 29 The particular ratio of N/S is achieved by the gearing 36-41 within the machine 11. To achieve the ratio of 31/6 the gears 36, 37 might have a ratio of 4:1 and this would be built into the machine. Accordingly, change gears 40, 41 would be selected with a gear ratio of 31:24. The overall ratio would then be 4/1 times 31/24 equals 31/6, the desired ratio. Table B shows the there are many more possible combinations available for use than in the rather limited selection of Table A. From observing the fifth column in Table B one will observe that the greatest number of thread starts are used when the ratio N/S is an irreducible fraction. If the ratio can be reduced then the number of thread starts used is less than the total number of starts on the rotary die 18. Such a case is illustrated by the third row where the ratio is 28/6. This can be reduced to 14/3 and only 14 of the 28 thread starts on the rotary die 18 are used for the starting point of workpieces. This would still be a considerable increase over the number of thread starts used in the prior art machine. The preferred method 1 and gear ratio of where either (N+1)/S or (N1)/S is an integer. In such case all of the thread starts are used.

The use of all of the thread starts is achieved in those cases in Table B where the ratio N/S is an irreducible fraction. In this manner each of the thread starts on the rotary die 18 is used for the start of thread rolling on workpieces in a particular sequence. For example, if the ratio is 26/5 then for 26,000 workpieces threaded, 1,000 are started on each of the 26 different thread starts around the periphery of the rotary die 18. This evenly spreads the wear around the die 18 and greatly increases the die life.

The large number of possible combinations, as illustrated in Table B, has another advantage of saving material in the construction of the rotary die 18. When a particular thread rolling machine 1 1 has been manufactured and shipped to a customer, the customer uses the rotary die and stationary die with which the machine was equipped to roll threads on workpieces. The dies eventually wear out or break down at the start of a thread and need to be replaced. The replacement die must, of course, fit that particular machine. A machine might have a nominal outside diameter of the rotary die 18 of 12 inches, for example. This can be varied slightly by a complementary change in thickness of the stationary die 19. The diameter of the rotary die 18 is a function of the pitch diameter of the workpiece for a constant radius of the stationary die 19. With a 12 inch nominal outer diameter of rotary die 18, the rotary die holder 14 might have a 7% inch diameter. In order to have a suitable radial thickness of the rotary die 18 for strength purposes, the outside diameter of die 18 might vary from 11 k to 12 k inches.

To choose an actual example, suppose -a.%-inch-13 United Screw thread is to be thread rolled. From a handbook one finds that this l-inch bolt has a pitch diameter of 0.450 inches with 13 threads per inch. The calculation to try to determine the number of thread starts and the diameter of the rotary die would then be to choose the 12 inch nominal diameter D compared with the diameter of the part d equals 0.450. This ratio is 26.7:1. If the prior art machine was geared to feed five workpieces per revoluation of the rotary die, then one would have tried, according to the prior art teaching, the fourth row on Table A. This row shows a ratio of N/S to be 25/5. This would require 25 starts on the rotary die and to produce a single start on the workpiece the ratio of D/d would have to be 25:1. This calculates to be 1 1.28 inches/ 0.450 inches. With a diameter D of the rotary die of 1 1.28 inches and subtracting 10.5 inches for the diameter of the rotary die holder 14, one finds the difference to be 0.78 inches or 0.39 inches radial thickness. This is too thin a rotary die, and it would not be strong enough to withstand the large rolling pressures. Accordingly, one would have to go to a ratio of N/S of 30/5 with 30 starts on the rotary die. Thirty times 0.450 equals 13.5 inches for the diameter D of the rotary die. Subtracting 10.5 inches the difference is 3 inches or 1.5 inches radial thickness of the rotary die. This is much too thick for economy and wastes material in the manufacture of such die. A satisfactory thickness is one-half to three-fourths inches wall thickness.

Under the present invention one could select the fifth row in Table B, a N/S ratio of 26/6. This is 26 starts on the rotary die and 26 times 0.450 equals 11.7 inches. Subtracting the 10.5 inches diameter of the die holder 14 gives 1.2 inches difference in diameter for a radial thickness of 0.6 inches. This is satisfactory for use in a rotary die 18. Alternatively, one could select the next row above in Table B for a N/S ratio of 27/6. Twentyseven times 0.450 equals 12.16 inches outer diameter of die 18 for a radial thickness of 0.83 inches. This is also satisfactory for the thickness of the rotary die. This shows that several different choices are available to achieve a satisfactory rotary die thickness to save material in the construction of such die.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A planetary thread rolling machine comprising, a frame,

a rotary die rotatable about an axis relative to said frame and having N starts of threads around the periphery thereof,

a second die on said frame,

a thread form on said second die substantially equal to that on said rotary die,

means to rotate said rotary die,v

means to feed a succession of workpieces to the area between said rotary and second dies,

and synchronizing means synchronizing the feeding of workpieces with a spacing S between workpieces where S is a given multiple of the peripheral spacing between thread starts on the rotary die and where the ratio of N/S is other than an integer.

2. A machine as set forth in claim 1, wherein said second die is a stationary die.

3. A machine as set forth in claim 1 wherein said second die has a multiple start thread form thereon.

4. A machine as set forth in claim 1 wherein N is an integer.

5. A machine as set forth in claim 1 wherein S is an integer.

6. A machine as set forth in claim 1 wherein said ratio of N/S is an irreducible fraction.

7. A machine as set forth in claim 1 wherein either the ratio N+l/S or N-1/S is an integer.

8. A machine as set forth in claim 1 wherein said second die has a multiple start thread form thereon with the peripheral spacing between thread starts substantially equal to the peripheral spacing between thread starts on said rotary die.

9. A machine as set forth in claim 1 wherein said synchronizing means establishes the feeding of workpieces at the starts of the threads on said rotary die.

10. The method of using a rotary and a second die to thread roll a thread on workpieces comprising the steps of,

providing on the rotary die a thread form of N multiple starts around the periphery thereof where N is a given plurality,

providing on the second die a thread form substantially equal to that on the rotary die,

rotating the rotary die about an axis for cooperation with the second die;

feeding to the area between the dies a succession of workpieces,

and synchronizing said feeding by spacing successive workpieces a distance S where S is a multiple of the number of starts on the rotary die and where the ratio N/S is other than an integer.

11. The method of claim 10, wherein said multiple S is an integer.

12. The method of claim 10, wherein the multiple N is an integer.

13. The method of claim 10, wherein the ratio of N/S is an irreducible fraction.

14. The method of claim 10, wherein either the ratio N+l/S or N-1/S is an integer.

18. The method of claim 10, wherein said thread form on the second die is a multiple start thread form. 19. The method of claim 10, wherein the thread form on the second die is a multiple start thread with the peripheral spacing between starts of threads thereon substantially equal to the peripheral spacing between starts of threads on the rotary die. 

1. A planetary thread rolling machine comprising, a frame, a rotary die rotatable about an axis relative to said frame and having N starts of threads around the periphery thereof, a second die on said frame, a thread form on said second die substantially equal to that on said rotary die, means to rotate said rotary die, means to feed a succession of workpieces to the area between said rotary and second dies, and synchronizing means synchronizing the feeding of workpieces with a spacing S between workpieces where S is a given multiple of the peripheral spacing between thread starts on the rotary die and where the ratio of N/S is other than an integer.
 2. A machine as set forth in claim 1, wherein said second die is a stationary die.
 3. A machine as set forth in claim 1 wherein said second die has a multiple start thread form thereon.
 4. A Machine as set forth in claim 1 wherein N is an integer.
 5. A machine as set forth in claim 1 wherein S is an integer.
 6. A machine as set forth in claim 1 wherein said ratio of N/S is an irreducible fraction.
 7. A machine as set forth in claim 1 wherein either the ratio N+1/S or N-1/S is an integer.
 8. A machine as set forth in claim 1 wherein said second die has a multiple start thread form thereon with the peripheral spacing between thread starts substantially equal to the peripheral spacing between thread starts on said rotary die.
 9. A machine as set forth in claim 1 wherein said synchronizing means establishes the feeding of workpieces at the starts of the threads on said rotary die.
 10. The method of using a rotary and a second die to thread roll a thread on workpieces comprising the steps of, providing on the rotary die a thread form of N multiple starts around the periphery thereof where N is a given plurality, providing on the second die a thread form substantially equal to that on the rotary die, rotating the rotary die about an axis for cooperation with the second die; feeding to the area between the dies a succession of workpieces, and synchronizing said feeding by spacing successive workpieces a distance S where S is a multiple of the number of starts on the rotary die and where the ratio N/S is other than an integer.
 11. The method of claim 10, wherein said multiple S is an integer.
 12. The method of claim 10, wherein the multiple N is an integer.
 13. The method of claim 10, wherein the ratio of N/S is an irreducible fraction.
 14. The method of claim 10, wherein either the ratio N+1/S or N-1/S is an integer.
 15. The method of claim 10, wherein the second die is a stationary die.
 16. The method of claim 15, wherein said feeding step includes feeding the workpieces to an entrance end of the stationary die.
 17. The method of claim 15, wherein said feeding step includes feeding workpieces at one of said multiple starts of said rotary die.
 18. The method of claim 10, wherein said thread form on the second die is a multiple start thread form.
 19. The method of claim 10, wherein the thread form on the second die is a multiple start thread with the peripheral spacing between starts of threads thereon substantially equal to the peripheral spacing between starts of threads on the rotary die. 